[PATCH v4 04/16] rust: io: perform conversions using `AsRepr`
From: Gary Guo
Date: Tue Sep 01 2026 - 14:33:50 EST
For types that are layout-compatible with an I/O capable type, we would
want the ability to use them directly for I/O operations. E.g.
bitfield! {
pub struct Foo(u32) {
...
}
}
#[repr(C)]
struct Bar {
foo: Foo,
}
let mmio: Mmio<'_, Bar> = ...;
io_read!(mmio, .foo)
Currently this feature is available from `register!()` macro but not
otherwise available with `io_read!`, `io_write!`. Support this by
performing conversions to I/O primitives via the `AsRepr`/`AsReprMut`
trait.
This makes the `IoLoc::IoType` and `Register::Storage` redundant; thus
remove them; also convert register methods to use the `read_val` and
`write_val` instead.
Reviewed-by: Alexandre Courbot <acourbot@xxxxxxxxxx>
Signed-off-by: Gary Guo <gary@xxxxxxxxxxx>
---
rust/kernel/bitfield.rs | 9 ++++
rust/kernel/io.rs | 128 ++++++++++++++++++++++++---------------------
rust/kernel/io/register.rs | 15 ------
rust/macros/io/register.rs | 2 -
4 files changed, 78 insertions(+), 76 deletions(-)
diff --git a/rust/kernel/bitfield.rs b/rust/kernel/bitfield.rs
index a0d089423f21..15c78790e151 100644
--- a/rust/kernel/bitfield.rs
+++ b/rust/kernel/bitfield.rs
@@ -346,6 +346,15 @@ fn from(val: $storage) -> $name {
Self::from_raw(val)
}
}
+
+ // SAFETY: `$name` is transparent over `$storage` and `$storage` has no interior mutability.
+ unsafe impl $crate::mem::AsRepr for $name {
+ // Normalize `$storage` to the canonical repr type in case it is signed.
+ type Repr = <$storage as $crate::mem::AsRepr>::Repr;
+ }
+
+ // SAFETY: `$name` is transparent over `$storage`.
+ unsafe impl $crate::mem::AsReprMut for $name {}
};
// Definitions requiring knowledge of individual fields: private and public field accessors,
diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
index 5ce9fd129068..18c71bd765b2 100644
--- a/rust/kernel/io.rs
+++ b/rust/kernel/io.rs
@@ -11,6 +11,10 @@
use crate::{
bindings,
+ mem::{
+ AsRepr,
+ AsReprMut, //
+ },
prelude::*,
ptr::{
Alignment,
@@ -226,6 +230,17 @@ fn io_view<'a, IO: Io<'a>, U>(
Ok(unsafe { IO::Backend::project_view(view, projected_ptr) })
}
+/// Returns the primitive view of a I/O view.
+#[inline]
+fn io_view_as_repr<'a, IO: Io<'a, Target = T>, T: AsRepr>(
+ this: IO,
+) -> <IO::Backend as IoBackend>::View<'a, T::Repr> {
+ let view = this.as_view();
+
+ // SAFETY: `AsRepr` guarantees layout compatibility.
+ unsafe { IO::Backend::project_view(view, IO::Backend::as_ptr(view).cast::<T::Repr>()) }
+}
+
/// I/O backends.
///
/// This is an abstract representation to be implemented by arbitrary I/O
@@ -353,15 +368,12 @@ fn copy_write<T: IntoBytes>(view: Self::View<'_, T>, value: T) {
///
/// - The valid `Base` to operate on. For most registers, this should be [`Region`].
/// - The offset to access (returned by [`IoLoc::offset`]),
-/// - The width of the access (determined by [`IoLoc::IoType`]),
-/// - The type `T` in which the raw data is returned or provided.
+/// - The type `T` in which the data is returned or provided.
///
-/// `T` and `IoLoc::IoType` may differ: for instance, a typed register has `T` = the register type
-/// with its bitfields, and `IoType` = its backing primitive (e.g. `u32`).
+/// `T` is not necessarily the type for underlying I/O operation. Methods that take `IoLoc` have `T:
+/// AsRepr` bound and the `<T as AsRepr>::Repr` type would be used to perform I/O and converted to
+/// `T` instead.
pub trait IoLoc<Base: ?Sized, T> {
- /// Size ([`u8`], [`u16`], etc) of the I/O performed on the returned [`offset`](IoLoc::offset).
- type IoType: Into<T> + From<T>;
-
/// Consumes `self` and returns the offset of this location.
fn offset(self) -> usize;
}
@@ -372,8 +384,6 @@ macro_rules! impl_usize_ioloc {
($($ty:ty),*) => {
$(
impl<const SIZE: usize> IoLoc<Region<SIZE>, $ty> for usize {
- type IoType = $ty;
-
#[inline(always)]
fn offset(self) -> usize {
self
@@ -498,10 +508,10 @@ fn try_cast<U>(self) -> Result<<Self::Backend as IoBackend>::View<'a, U>>
#[inline]
fn read_val(self) -> Self::Target
where
- Self::Backend: IoCapable<Self::Target>,
- Self::Target: Sized,
+ Self::Target: AsReprMut,
+ Self::Backend: IoCapable<<Self::Target as AsRepr>::Repr>,
{
- Self::Backend::io_read(self.as_view())
+ Self::Target::from_repr(Self::Backend::io_read(io_view_as_repr(self)))
}
/// Write a value to I/O.
@@ -520,10 +530,10 @@ fn read_val(self) -> Self::Target
#[inline]
fn write_val(self, value: Self::Target)
where
- Self::Backend: IoCapable<Self::Target>,
- Self::Target: Sized,
+ Self::Target: AsRepr,
+ Self::Backend: IoCapable<<Self::Target as AsRepr>::Repr>,
{
- Self::Backend::io_write(self.as_view(), value)
+ Self::Backend::io_write(io_view_as_repr(self), Self::Target::into_repr(value))
}
/// Copy-read from I/O memory.
@@ -645,7 +655,7 @@ fn copy_to_slice(self, data: &mut [u8])
#[inline(always)]
fn try_read8(self, offset: usize) -> Result<u8>
where
- usize: IoLoc<Self::Target, u8, IoType = u8>,
+ usize: IoLoc<Self::Target, u8>,
Self::Backend: IoCapable<u8>,
{
self.try_read(offset)
@@ -655,7 +665,7 @@ fn try_read8(self, offset: usize) -> Result<u8>
#[inline(always)]
fn try_read16(self, offset: usize) -> Result<u16>
where
- usize: IoLoc<Self::Target, u16, IoType = u16>,
+ usize: IoLoc<Self::Target, u16>,
Self::Backend: IoCapable<u16>,
{
self.try_read(offset)
@@ -665,7 +675,7 @@ fn try_read16(self, offset: usize) -> Result<u16>
#[inline(always)]
fn try_read32(self, offset: usize) -> Result<u32>
where
- usize: IoLoc<Self::Target, u32, IoType = u32>,
+ usize: IoLoc<Self::Target, u32>,
Self::Backend: IoCapable<u32>,
{
self.try_read(offset)
@@ -675,7 +685,7 @@ fn try_read32(self, offset: usize) -> Result<u32>
#[inline(always)]
fn try_read64(self, offset: usize) -> Result<u64>
where
- usize: IoLoc<Self::Target, u64, IoType = u64>,
+ usize: IoLoc<Self::Target, u64>,
Self::Backend: IoCapable<u64>,
{
self.try_read(offset)
@@ -685,7 +695,7 @@ fn try_read64(self, offset: usize) -> Result<u64>
#[inline(always)]
fn try_write8(self, value: u8, offset: usize) -> Result
where
- usize: IoLoc<Self::Target, u8, IoType = u8>,
+ usize: IoLoc<Self::Target, u8>,
Self::Backend: IoCapable<u8>,
{
self.try_write(offset, value)
@@ -695,7 +705,7 @@ fn try_write8(self, value: u8, offset: usize) -> Result
#[inline(always)]
fn try_write16(self, value: u16, offset: usize) -> Result
where
- usize: IoLoc<Self::Target, u16, IoType = u16>,
+ usize: IoLoc<Self::Target, u16>,
Self::Backend: IoCapable<u16>,
{
self.try_write(offset, value)
@@ -705,7 +715,7 @@ fn try_write16(self, value: u16, offset: usize) -> Result
#[inline(always)]
fn try_write32(self, value: u32, offset: usize) -> Result
where
- usize: IoLoc<Self::Target, u32, IoType = u32>,
+ usize: IoLoc<Self::Target, u32>,
Self::Backend: IoCapable<u32>,
{
self.try_write(offset, value)
@@ -715,7 +725,7 @@ fn try_write32(self, value: u32, offset: usize) -> Result
#[inline(always)]
fn try_write64(self, value: u64, offset: usize) -> Result
where
- usize: IoLoc<Self::Target, u64, IoType = u64>,
+ usize: IoLoc<Self::Target, u64>,
Self::Backend: IoCapable<u64>,
{
self.try_write(offset, value)
@@ -727,7 +737,7 @@ fn try_write64(self, value: u64, offset: usize) -> Result
#[inline(always)]
fn read8(self, offset: usize) -> u8
where
- usize: IoLoc<Self::Target, u8, IoType = u8>,
+ usize: IoLoc<Self::Target, u8>,
Self::Backend: IoCapable<u8>,
{
self.read(offset)
@@ -739,7 +749,7 @@ fn read8(self, offset: usize) -> u8
#[inline(always)]
fn read16(self, offset: usize) -> u16
where
- usize: IoLoc<Self::Target, u16, IoType = u16>,
+ usize: IoLoc<Self::Target, u16>,
Self::Backend: IoCapable<u16>,
{
self.read(offset)
@@ -751,7 +761,7 @@ fn read16(self, offset: usize) -> u16
#[inline(always)]
fn read32(self, offset: usize) -> u32
where
- usize: IoLoc<Self::Target, u32, IoType = u32>,
+ usize: IoLoc<Self::Target, u32>,
Self::Backend: IoCapable<u32>,
{
self.read(offset)
@@ -763,7 +773,7 @@ fn read32(self, offset: usize) -> u32
#[inline(always)]
fn read64(self, offset: usize) -> u64
where
- usize: IoLoc<Self::Target, u64, IoType = u64>,
+ usize: IoLoc<Self::Target, u64>,
Self::Backend: IoCapable<u64>,
{
self.read(offset)
@@ -775,7 +785,7 @@ fn read64(self, offset: usize) -> u64
#[inline(always)]
fn write8(self, value: u8, offset: usize)
where
- usize: IoLoc<Self::Target, u8, IoType = u8>,
+ usize: IoLoc<Self::Target, u8>,
Self::Backend: IoCapable<u8>,
{
self.write(offset, value)
@@ -787,7 +797,7 @@ fn write8(self, value: u8, offset: usize)
#[inline(always)]
fn write16(self, value: u16, offset: usize)
where
- usize: IoLoc<Self::Target, u16, IoType = u16>,
+ usize: IoLoc<Self::Target, u16>,
Self::Backend: IoCapable<u16>,
{
self.write(offset, value)
@@ -799,7 +809,7 @@ fn write16(self, value: u16, offset: usize)
#[inline(always)]
fn write32(self, value: u32, offset: usize)
where
- usize: IoLoc<Self::Target, u32, IoType = u32>,
+ usize: IoLoc<Self::Target, u32>,
Self::Backend: IoCapable<u32>,
{
self.write(offset, value)
@@ -811,7 +821,7 @@ fn write32(self, value: u32, offset: usize)
#[inline(always)]
fn write64(self, value: u64, offset: usize)
where
- usize: IoLoc<Self::Target, u64, IoType = u64>,
+ usize: IoLoc<Self::Target, u64>,
Self::Backend: IoCapable<u64>,
{
self.write(offset, value)
@@ -843,11 +853,12 @@ fn write64(self, value: u64, offset: usize)
#[inline(always)]
fn try_read<T, L>(self, location: L) -> Result<T>
where
+ T: AsReprMut,
L: IoLoc<Self::Target, T>,
- Self::Backend: IoCapable<L::IoType>,
+ Self::Backend: IoCapable<<T as AsRepr>::Repr>,
{
- let view = io_view::<Self, L::IoType>(self, location.offset())?;
- Ok(Self::Backend::io_read(view).into())
+ let view = io_view::<Self, T>(self, location.offset())?;
+ Ok(view.read_val())
}
/// Generic fallible write with runtime bounds check.
@@ -876,12 +887,12 @@ fn try_read<T, L>(self, location: L) -> Result<T>
#[inline(always)]
fn try_write<T, L>(self, location: L, value: T) -> Result
where
+ T: AsRepr,
L: IoLoc<Self::Target, T>,
- Self::Backend: IoCapable<L::IoType>,
+ Self::Backend: IoCapable<<T as AsRepr>::Repr>,
{
- let view = io_view::<Self, L::IoType>(self, location.offset())?;
- let io_value = value.into();
- Self::Backend::io_write(view, io_value);
+ let view = io_view::<Self, T>(self, location.offset())?;
+ view.write_val(value);
Ok(())
}
@@ -920,9 +931,10 @@ fn try_write<T, L>(self, location: L, value: T) -> Result
#[inline(always)]
fn try_write_reg<T, L, V>(self, value: V) -> Result
where
+ T: AsRepr,
L: IoLoc<Self::Target, T>,
V: LocatedRegister<Self::Target, Location = L, Value = T>,
- Self::Backend: IoCapable<L::IoType>,
+ Self::Backend: IoCapable<<T as AsRepr>::Repr>,
{
let (location, value) = value.into_io_op();
@@ -954,16 +966,13 @@ fn try_write_reg<T, L, V>(self, value: V) -> Result
#[inline(always)]
fn try_update<T, L, F>(self, location: L, f: F) -> Result
where
+ T: AsReprMut,
L: IoLoc<Self::Target, T>,
- Self::Backend: IoCapable<L::IoType>,
+ Self::Backend: IoCapable<<T as AsRepr>::Repr>,
F: FnOnce(T) -> T,
{
- let view = io_view::<Self, L::IoType>(self, location.offset())?;
-
- let value: T = Self::Backend::io_read(view).into();
- let io_value = f(value).into();
- Self::Backend::io_write(view, io_value);
-
+ let view = io_view::<Self, T>(self, location.offset())?;
+ view.write_val(f(view.read_val()));
Ok(())
}
@@ -991,11 +1000,12 @@ fn try_update<T, L, F>(self, location: L, f: F) -> Result
#[inline(always)]
fn read<T, L>(self, location: L) -> T
where
+ T: AsReprMut,
L: IoLoc<Self::Target, T>,
- Self::Backend: IoCapable<L::IoType>,
+ Self::Backend: IoCapable<<T as AsRepr>::Repr>,
{
- let view = io_view_assert::<Self, L::IoType>(self, location.offset());
- Self::Backend::io_read(view).into()
+ let view = io_view_assert::<Self, T>(self, location.offset());
+ view.read_val()
}
/// Generic infallible write with compile-time bounds check.
@@ -1022,12 +1032,12 @@ fn read<T, L>(self, location: L) -> T
#[inline(always)]
fn write<T, L>(self, location: L, value: T)
where
+ T: AsRepr,
L: IoLoc<Self::Target, T>,
- Self::Backend: IoCapable<L::IoType>,
+ Self::Backend: IoCapable<<T as AsRepr>::Repr>,
{
- let view = io_view_assert::<Self, L::IoType>(self, location.offset());
- let io_value = value.into();
- Self::Backend::io_write(view, io_value);
+ let view = io_view_assert::<Self, T>(self, location.offset());
+ view.write_val(value)
}
/// Generic infallible write of a fully-located register value.
@@ -1064,9 +1074,10 @@ fn write<T, L>(self, location: L, value: T)
#[inline(always)]
fn write_reg<T, L, V>(self, value: V)
where
+ T: AsRepr,
L: IoLoc<Self::Target, T>,
V: LocatedRegister<Self::Target, Location = L, Value = T>,
- Self::Backend: IoCapable<L::IoType>,
+ Self::Backend: IoCapable<<T as AsRepr>::Repr>,
{
let (location, value) = value.into_io_op();
@@ -1098,14 +1109,13 @@ fn write_reg<T, L, V>(self, value: V)
#[inline(always)]
fn update<T, L, F>(self, location: L, f: F)
where
+ T: AsReprMut,
L: IoLoc<Self::Target, T>,
- Self::Backend: IoCapable<L::IoType>,
+ Self::Backend: IoCapable<<T as AsRepr>::Repr>,
F: FnOnce(T) -> T,
{
- let view = io_view_assert::<Self, L::IoType>(self, location.offset());
- let value: T = Self::Backend::io_read(view).into();
- let io_value = f(value).into();
- Self::Backend::io_write(view, io_value);
+ let view = io_view_assert::<Self, T>(self, location.offset());
+ view.write_val(f(view.read_val()));
}
}
diff --git a/rust/kernel/io/register.rs b/rust/kernel/io/register.rs
index 6a19552ffb95..45d2e73a92e7 100644
--- a/rust/kernel/io/register.rs
+++ b/rust/kernel/io/register.rs
@@ -117,9 +117,6 @@
/// Trait implemented by all registers.
pub trait Register: Sized {
- /// Backing primitive type of the register.
- type Storage: Into<Self> + From<Self>;
-
/// Start offset of the register.
///
/// The interpretation of this offset depends on the type of the register.
@@ -135,8 +132,6 @@ impl<const SIZE: usize, T> IoLoc<Region<SIZE>, T> for ()
where
T: FixedRegister,
{
- type IoType = T::Storage;
-
#[inline(always)]
fn offset(self) -> usize {
T::OFFSET
@@ -149,8 +144,6 @@ impl<const SIZE: usize, T> IoLoc<Region<SIZE>, T> for T
where
T: FixedRegister,
{
- type IoType = T::Storage;
-
#[inline(always)]
fn offset(self) -> usize {
T::OFFSET
@@ -174,8 +167,6 @@ impl<const SIZE: usize, T> IoLoc<Region<SIZE>, T> for FixedRegisterLoc<T>
where
T: FixedRegister,
{
- type IoType = T::Storage;
-
#[inline(always)]
fn offset(self) -> usize {
T::OFFSET
@@ -246,8 +237,6 @@ impl<const SIZE: usize, T, B> IoLoc<Region<SIZE>, T> for RelativeRegisterLoc<T,
T: RelativeRegister,
B: RegisterBase<T::BaseFamily> + ?Sized,
{
- type IoType = T::Storage;
-
#[inline(always)]
fn offset(self) -> usize {
RelativeRegisterLoc::offset(self)
@@ -289,8 +278,6 @@ impl<const SIZE: usize, T> IoLoc<Region<SIZE>, T> for RegisterArrayLoc<T>
where
T: RegisterArray,
{
- type IoType = T::Storage;
-
#[inline(always)]
fn offset(self) -> usize {
T::OFFSET + self.0 * T::STRIDE
@@ -377,8 +364,6 @@ impl<const SIZE: usize, T, B> IoLoc<Region<SIZE>, T> for RelativeRegisterArrayLo
T: RelativeRegisterArray,
B: RegisterBase<T::BaseFamily> + ?Sized,
{
- type IoType = T::Storage;
-
#[inline(always)]
fn offset(self) -> usize {
self.0.offset() + self.1 * T::STRIDE
diff --git a/rust/macros/io/register.rs b/rust/macros/io/register.rs
index 83ba4dd75ab3..9b92c8099edd 100644
--- a/rust/macros/io/register.rs
+++ b/rust/macros/io/register.rs
@@ -213,8 +213,6 @@ pub(crate) fn register(def: RegDef) -> Result<TokenStream> {
);
impl ::kernel::io::register::Register for #name {
- type Storage = #storage;
-
const OFFSET: usize = #offset;
}
));
--
2.54.0